Apparatus for the manufacture of formaldehyde



Sept 3 1945 P. scHmELER Erm. 2,406,908

PPARATUS FOR THE MANUFAC'HIRE 0F FORMALDEHYDE Filed Nov; 28, 1942 2`Sheets-Sheet 1 A BY 4 34 f A'rroRNv V sq. 3, 194e.

P. s'cHlDELER er AL APPARATUS FOR THE MANUFACTURE OF FORMALDEHYDE' FiledNOV. 28, 1942 2 Sheets-Sheet 2 l I INVENTORS PMT/Pf fcf//a4 if? PatentedSept. 1946 APPARATUS Fon 'rma MANUFACTUBE 0F FORMALDEHYDE PierreSchldeler, New York, and Ralph S. Bichax-dson, Scarsdale, N. Y.,assigner; to Chemical ConstructionV Corporation, New York, N. Y., a

corporation of Delaware Application November 28, 1942, Serial No.V467,258

' z claims. (ci. ca -ass) This invention relates to the manufacture offormaldehyde by the catalytic conversion or oxidation of methanol vaporandhas as its object 1 the provision of a method and apparatus forcontrolling the reaction temperature in relatively large sizes of burnerunits. .'I'he method is further characterized by the provision of meansfor the sudden ycooling of the products of the reaction;

In modern formaldehyde manufacture it is now the practice to carry outthe partial combustion `of methanol inthe presence ofcatalystscontaining copper, silver or other mild oxidation,

catalysts. The reaction between methanol and oxygen may produce not onlyformaldehyde and water but also carbon oxides, 'water and carbon if thetemperature of the reaction is not maintained suitably. It is customary,therefore, to

control the heat of reaction by circulating through the catalyst amethanol-air mixture containing a considerable excess 'of methanol vaporand to use'` a large number of converters of relatively small dimensionsand low capacity so thaty the heat generated by the reaction may bedissipated from the surface of the converters without causing anVundesirable high catalyst temperature.

. The necessity of ei'nploying7 a large number of converters of smallsize is avoided bythe present invention, which provides a method andappara-7 tus for,obtaining close control of the reaction temperaturesthroughout the entire volume of the catalyst bed. We have found that thecourse of the partial oxidation of methanol -to formaldehyde in thepresence of a catalyst such as copper,

silver and the like can Jbe closely controlled at `the optimumtemperature valuesby employing a catalyst-bed in the form of arelatively narrow annulus through which the reaction gas mixture ispassed longitudinally while' applying a temperature regulating gas toone or both of the outer surfaces of the annulus. This method providesboth for the application of a cooling gas to prevent undue temperaturerise during operation oi the converter and the application of a heatinggas inthe same manner when starting up the converter or at any othertime that additional heating may, be necessary. By this method it ispossible to obtain a large dailyoutput of formaldehyde in a converter ofvery large unit .I

capacity, thus simplifying the operating conditions within the plant. Infact, there is no present limitation to the size of unit which may beconstructed.

The process of our invention therefore comprises the steps of passing agas mixture containgas with or without diluents of anydesired type,longitudinally through a relatively narow vertical catalystannulus whilepassing a stream of temperature regulating gas such as `hot or coldairor hot products of combustion at relatively high .velocity in heatexchange relation with one or both of the vertical surfaces of theannulus, Y preferably in a direction opposite to that of the ow of thereaction gas mixture.v The hot gas mix-ture from the catalyst isthenpassed into a cooler which is preferably constructed as any integralpart of the converter, and after the preliminary cooling step themixture may-be passed to a recovery system adapted to-absorb theremaining formaldehyde in water andto recover V.for reusel anyunconverted methanol if desired.,

Our invention will be illustrated in greater detail withreference to theaccompanying draw-y ings, which show a catalytic converterl employingthe principles thereof. This converter also contains a number offeatures of design and construction which constitute an important partof.4 ,our invention, as will subsequently be explained.

Qn the drawings,

Figfl is a diagrammatic elevation of one embodiment ofthe converter ofour invention in which the internal assembly is shown in dottei lines;`

Fig. 251s a section on the une z-.t cf Fig, 1;`

and,V v

Fig. 3 is a vertical section of a part of the assembly of Fig. 1 on aslightly larger scale.

Referring to Figs. 1 and 3 the' converter designated generally byreference numeral I comprises two vertical concentric shells 2 and 3which denne a vertical annulus I containing an annular bed of catalystof any suitable composition. The outer shell 2 is flanged at its upperand lower edges 6 and 1 while the inner shell 3 is extended upwardlybeyond the outer shell and terminates againsta. cover plate 8 havingansoutlet I9 therein. The outer and inner shells 2 and 3 are rigidlyfastened together by twosets of radial bars 9 asy is more clearly shownin Fig. 2. An annular screen i0 divided in sections is supported on the'lower of the 4two 'setsof bars 9 and serves to retain the catalyst whilepermitting .passage =of the oxidation products therethrough.

The inner shell 3 'containsit removable baille structure I3 which isseparated from the` gases leaving the catalyst by partition i i and isadapted to directand maintain a ilow of temperature regulating gas atrelatively high velocity over the inner ysurface of the innershell I ina direction countercurrent to that of the ilow of the reaction gasesover the catalyst.

The vertical baiiie structure consists essentially of a vertical tubeI4, the lower end of which is enlarged as at I to form with the tube I arelatively narrow annular channel I6. The upper end of the tube I4 isprovided with gasinlet I1 while a series of perforations I8 at itsenlarged.l lower end serve to project streams of cooling gas against theinner wall of the annulus formed by the shell 3 at an area adjacent thelower part of the catalyst. The temperature regulating gas then passesupwardly through the narrow channel I6 and is removed through the outletI9.

The reaction gas mixture is admitted to the converter throughgas-distributing pipe 20 which surrounds a flanged cylindrical shell 2|mounted on the upper flange 6 of the outer converter shell 3 and whichis provided with a series of holes 23 of suitable diameter for evendistribution of the incoming gas mixture. The upper part of thecylindrical shell 2I is turned inwardly as lat 24 and provided with apacking ring 26 to flt tightly against the upper portion of the innerconverter shell 3 and form therewith a gas inlet passage incommunication with the catalyst chamber 4.

In order to preheat the catalyst to reaction vtemperatures in startingup the converter, the

' cooler 2l. -A valve in the outlet pipe 36 permits a close control inthe back pressure of the converter, which is an important factor when`several converters are operated in parallel, and the immediate coolingof the hot reacted gases per-- mits the use of a control valve ofordinary construction at this point.

Because of the extremely uniform distribution of the reaction gasmixture over a single annular central bale structure It is provided witha gas inlet pipe 26 which terminates in a combustion chamber 21 formedby the enlarged lower portion 'I5 of the pipe I4. Hydrocarbon gas orother fuel entering through the pipe 26 is ignited through a port (notshown) and burned by air admitted through the inlet pipe I1, and thepassage of the hot products of the chamber 21 and holes heats thecatalyst to the proper temperature. Heat may be applied to the catalystin this manner when starting up the converter and may. also combustionythrough A I8 and channel I6 be employed whenever the partial combustionof methanol is not suiiicient to heat the catalyst to the desiredoperating temperature.

Improved yields of formaldehyde accompanied by considerably smallerquantities of undesirable byproducts are obtained when the hot reactiongas mixture from" the catalyst is cooled immediately Vwith a minimum ofexposure to hot catalytic surfaces. We therefore provide a cooler 28 Vasa part of the catalytic converter. This cooler may advantageously be inthe form of a tubular condenser provided with a water-inlet 29, a wateroutlet 30 and a large number of vertical cooling tubes extending betweenupper and lower headers 32 and 33 and serving to produce a rapid coolingof the reacted gases. condensate formed in the tubes 3l can be removedthrough pipe 34 while the relatively cooled gases are taken oif throughoutlet pipe 35 and may be passed to any suitable absorbing apparatus forthe separation of unconverted methanol and recovery of formaldehyde. Insome cases a direct cooler in the form of a small packed tower providedwith means for recirculating water or cooled condensate over the packingmay be lsubstituted for the catalyst of uniform depth it is possible toload the catalyst heavily with a gas mixture having .those ratios ofmethanol to oxygen or air which are best suited for the maximum yieldsof formaldehyde with minimum quantities of byproduots. The temperatureconditions resulting from the use of such mixtures can be adjusted toany desired degree by regulating the quantity and temperature of the`air introduced through the air inlet I1.

From the foregoing detailed description it is evident that the convertershown on the drawings illustrate in detail the principles of ourinvention. By providing the catalyst in the form of a, vertical annuluswe obtain a maximum of cooling surface consistent with the volume ofcatalyst necessary for large scale production, and it should be notedthat ilns or other cooling elements may be attached to the surface ofthe outer converter shell 2 opposite the catalyst 5 if additionalcooling should prove to be necessary or desirable. The reaction gasmixture introduced through the valve 21 is evenly distributed by theorifices 23 in the inlet section 2I of the converter and passesvertically through the entire depth of the annular catalyst bed, whileair or other gas under slightly positive pressure is introduced at I'I'and passes through the opening I8 and upwardly lthrough the narrowchannel I8 in counterc'urrent heat exchanging relation with the reactiongas mixture in the an-y nular passage 4. y

What we claim is:

1. Apparatus for the manufacture of formaldehyde comprising incombination inner and outer concentric shells defining al catalystannulus, means for passing a reaction gas mixture containing methanoland oxygen vertically through said catalyst annulus, and a vertical tubewithin said inner shell having openings at the lower end thereof adaptedto conduct a ow of a temperature regulating gas along the inner surfaceof said inner shell adjacent the catalystcontaining area.

2. Apparatus for the manufacture of formaldehyde comprising incombination inner and outer concentric shells defining a catalystcontaining annulus, means withiny said inner shell for passing a ow oftemperature regulating gas along the inner surface of said shellopposite the catalyst-containing annulus, and a cooler locatedimmediately following said catalyst-containing annulus ,and adapted forshock cooling of the reacted gases. l

PIERRE SCI-IIDELER. RALPH S. RICHARDSON.

